153 publications from this institution
Collapse performance of two existing buildings was investigated through experimental testing and computational simulations. Each building was tested in the field by physically removing four first-story perimeter columns from each building prior to building's scheduled demolition. Linear static and nonlinear dynamic analyses were performed using two- and three-dimensional building frame models. Experimental data from the field tests of two buildings were used to compare and verify the computational analyses. The measured strain data compared relatively well with the analysis results. In particular, 3-D model was more accurate than the 2-D model. The strain values calculated from the nonlinear dynamic analysis were smaller than those from the linear static analysis, and were closer to the measured strains. Also, linear static analysis resulted in larger remandto- capacity ratios (DCR) and vertical displacements than nonlinear dynamic analysis for both 2-D and 3-D models.
The main goal of this research is to better understand progressive collapse mechanisms of buildings, and to evaluate the current modeling and analysis techniques and design methodologies. Field experiments and numerical simulations were performed to investigate the progressive collapse potential of several reinforced concrete and steel frame buildings. Up to four first-story columns were physically removed from the buildings to understand the subsequent load redistribution within each building. Experimental data from the field tests were used to compare and verify the computational models and analysis results. Due to the scarcity of data from full-scale tests, the experimental data of this research is a valuable addition to the state of knowledge on progressive collapse of buildings. The design guidelines typically recommend simplified analysis procedures involving instantaneous removal of specified critical columns in a building. This research investigates the effectiveness of such commonly used progressive collapse evaluation and design methodologies through numerical simulation and experimental data.
Reinforcement slip in footings and beam-column joint regions can make a significant contribution to the total lateral displacement of a reinforced concrete structure. In this paper, a model for the prediction of lateral deformation of a column due to reinforcement slip in the anchorage zone is presented. The model employs a stepped bond stress along the embedded length of the reinforcing bar that allows for efficient computation of displacements due to slip. A method for computing slip when a reinforcing bar is stressed to its unloaded end and a corresponding failure criterion are presented. Procedures for calculating slip in hooked bars are also outlined. The proposed model is compared with five other commonly-used models found in the literature against three independent sets of test data. Considering its simplicity and computational efficiency, the proposed model predicts slip displacements reasonably well.
Postearthquake reconnaissance and recent research on seismic risk analysis have shown that nonductile concrete frame structures are much more susceptible to collapse than modern code-conforming frames. The performance-based assessment paradigm has been a persistent research theme over the last decade within the earthquake engineering community in order to estimate seismic fragilities and earthquake loss for these nonductile concrete frames. This paper proposes a nonlinear performance-based methodology to evaluate different retrofit methods considering hazard level, target performance levels, and life-cycle cost estimates. The structural performance is the main parameter considered for the optimization, although a life-cycle cost analysis is also presented. As a case study, the longitudinal frame of an existing building was modeled considering the effect of flexural-shear-axial load interaction in order to capture column shear and axial failures. The presented performance-based procedure identifies the most economic retrofit solution that satisfies structural response requirements for a given performance level.
Findings and conclusions of experimental and computational studies are presented regarding the effect of longitudinal bending on joints in rigid (reinforced concrete) and flexible (corrugated steel and thermoplastic) culverts. Two joint types are examined – those releasing the longitudinal bending moments (denoted ‘moment-release joints’) like gasketted bell and spigot joints, and those transferring them (denoted ‘moment-transfer joints’) such as band connections. Structural design requires evaluation of the ability to transfer vertical shear force across moment-release and moment-transfer joints, longitudinal bending moments across moment-transfer joints, and for moment-release joints to accommodate rotations. Both field performance and laboratory experiments are used to evaluate the behavior of jointed pipe systems for four different diameters, two different cover depths, and response to surface loads in a variety of positions. Different approaches are investigated for analysis of the structural behavior of joints to determine thrust, moment and rotation across joints. One approach considering two beams supported by elastic springs is used to develop a simplified design procedure. A second design approach involves finite element analysis using beam-on-elastic-spring modeling. Design examples are presented, and preliminary tests of the capacity of three of the test pipes indicate that these products satisfy the structural design requirements being proposed.
Many historical and new masonry minarets were damaged or collapsed during the 1999 earthquakes in Kocaeli and Duzce, Turkey. These and other recent earthquakes not only caused loss of property but also loss of many lives. The structural failures and resulting casualties have led to discussion and investigation of potential reasons for poor seismic performance of masonry minarets. The primary goal of this study is to review the construction practices for historical and new masonry minarets in Turkey and to discuss the seismic damage observed in those structures. The architectural and structural properties of contemporary and historical Ottoman minarets and their components are presented. For example, a very old special technique for reinforcing and linking adjacent stone blocks with iron pieces in the vertical and horizontal directions is discussed. The structural damage examples are used to better understand the reasons for the observed failure mechanisms. It is concluded that the transition region between the square minaret boot and cylindrical body was most vulnerable to damage, and the iron clamps used in historical minarets effectively prevented structural damage.
Parameters affecting the shear strength of reinforced concrete columns having a rectangular cross section and light transverse reinforcement are investigated using data from numerous column tests. A new model is proposed to predict the column shear strength based on theoretical formulations and experimental evidence. The proposed shear strength equation includes contributions from the concrete and transverse reinforcement. Primary parameters in the shear strength model are the column cross-sectional dimensions, concrete compressive strength, column aspect ratio, axial load, and displacement ductility demand. The proposed model is compared with other shear strength models using the available column test data and is shown to result in improved accuracy. A conservative shear strength model for use in design and assessment is proposed based on statistical evaluation of computed and actual shear strengths.
Reinforced concrete jacketing is one of the most frequently used methods for strengthening of reinforced concrete (RC) columns. A large number of experimental studies have been carried out to investigate the effectiveness of repair and strengthening techniques and interface treatment on the response of concrete jacketed columns. However, the effects of potential damage in existing column and quality of core concrete on the response of jacketed RC columns have not been investigated. One of the main goals of this study is to examine how the material properties of the existing column affect the overall response of the jacketed RC columns. Two computer models were developed and nonlinear analyses were performed to determine the moment-curvature relationships and axial load-moment interaction diagrams of concrete jacketed RC cross sections. The effects of material strength and magnitude of axial loads were investigated. It is determined that the strength of core concrete has no effect on the response of concrete jacketed RC columns under lower axial loads while it increases the strength and reduces the ductility under higher axial load levels
Summary Suspended buildings typically have a core as the primary and suspended floors as the secondary structures. These configurations offer visual transparency, smaller vertical components, and seismic attenuation via the primary–secondary structure interaction. Such attenuation is further enhanced by the modularization of the suspended segment which allows large drifts but prevents them from causing damage. Previously conducted shake‐table tests have confirmed these features. However, how the component performance contributes to system performance has not been quantitated. To address this gap, fragility analyses are conducted for 10‐story experimentally validated models with optimized supplemental dampers and inter‐module stiffness. Multiple limit state functions are proposed to provide a full account of damage sources. Additionally, a mapping rule from the component‐level to the system‐level limit states is developed which captures the influence of damage distribution on system‐level limit states. Results for the uncontrolled suspended building indicate that for the PGV of 0.5 m/s, the failure probabilities of the repairable and life safety limit states are 97% and 83%, respectively. These probabilities are 92% and 27% for the frame structure with viscous dampers, 58% and 5% for the passive‐controlled modularized suspended building system (MSBS), and 45% and 3% for MSBS with optimal vertical distributions of modularized secondary structure.
First Name is required invalid characters Last Name is required invalid characters Email Address is required Invalid Email Address Invalid Email Address
Load-rating factors are used to evaluate the service life or safety of culverts based on the culvert wall strength and soil cover depth over the culvert. Current culvert load-rating methods have deficiencies in identifying potential critical conditions of corrugated metal culverts. Current load-rating procedures do not provide explicit guidance to the engineer for load rating and evaluation of culvert condition. To ensure good performance over the design life, corrugated metal culverts must be designed and regularly evaluated using an effective load-rating method. The main objective of this study was to investigate the effectiveness of current load-rating procedures. Recommendations are made to improve the analysis and evaluation procedures for corrugated metal culverts. The proposed load-rating procedure is based on an extensive review of load-rating procedures and design practices, experimental data, and theoretical investigations. The proposed method does not include a rating factor for cover depth. However, the design cover depth is required to be checked during the initial design stage to ensure structural stability. New capacity reduction factors are introduced for culvert wall and seam, which require different appraisals for wall and seam during annual inspections. The effect of external live loads is not included in the proposed load-rating procedure for deep culverts and for culverts subjected to low live load stresses. Field data from 39 in-service culverts showed that the proposed load-rating procedure is effective in evaluation of the existing condition of culverts.
Six reinforced concrete beam-column joint specimens were constructed and tested under reverse cyclic loading to failure. The six specimens were divided into three groups, each group representing a different joint design. The main objectives of this study are to investigate the response of joints with three different design, reinforcement detailing and beam strengths, and to evaluate and compare the responses of beam-column joints reinforced with traditional steel rebar and a recently proposed steel reinforcement called prefabricated cage system (PCS). Each of the three test specimen designs included equivalent amount of steel reinforcement and had virtually identical details. The results of the research show that the PCS reinforced joints had a slightly higher strength and significantly larger deformation capacity than the equivalent rebar reinforced joints.
No abstract is provided for this article.
Load-rating factors are used to evaluate the service life or safety of culverts based on the culvert wall strength and soil cover depth over the culvert. Current culvert load-rating methods have deficiencies in identifying potential critical conditions of corrugated metal culverts. Current load-rating procedures do not provide explicit guidance to the engineer for load rating and evaluation of culvert condition. To ensure good performance over the design life, corrugated metal culverts must be designed and regularly evaluated using an effective load-rating method. The main objective of this study was to investigate the effectiveness of current load-rating procedures. Recommendations are made to improve the analysis and evaluation procedures for corrugated metal culverts. The proposed load-rating procedure is based on an extensive review of load-rating procedures and design practices, experimental data, and theoretical investigations. The proposed method does not include a rating factor for cover depth. However, the design cover depth is required to be checked during the initial design stage to ensure structural stability. New capacity reduction factors are introduced for culvert wall and seam, which require different appraisals for wall and seam during annual inspections. The effect of external live loads is not included in the proposed load-rating procedure for deep culverts and for culverts subjected to low live load stresses. Field data from 39 in-service culverts showed that the proposed load-rating procedure is effective in evaluation of the existing condition of culverts.
This study investigates the accuracy of FEMA 356 shear and flexure modeling procedures for reinforced concrete (RC) columns and beam-column joints with poorly detailed or insufficient reinforcement. Following the FEMA 356 guidelines, generalized flexure and shear force-deformation relations were developed and compared with the experimental data from 26 column specimens and 17 beam-column joint specimens. Specifically, the measured and predicted responses were compared and evaluated: at yield displacement and the corresponding lateral load, lateral load and displacement at ultimate, and at axial load failure. In general, while the FEMA 356 models predict the lateral strength of columns reasonably well, they underestimate the shear strength of beam column joints. The predicted initial stiffness and deformations at both yield and ultimate are conservative for columns.
This study investigates the structural performance of industrial buildings following the February 6, 2023, earthquakes in Kahramanmaras, Turkey, focusing mainly on industrial zones. Causes of damage and damage levels were evaluated for 389 industrial structures, including precast concrete and steel structures. This research demonstrates the need for improved construction practices, advanced seismic design, and quality control. Commonly observed structural damage is highlighted. Identifying the critical common structural damage types is essential to developing effective mitigation strategies and enhancing earthquake resilience. It is concluded that advanced seismic design practices can significantly improve the overall structural performance, resilience, and functional recovery.
An unusually large number of minarets, which are slender tower structures, collapsed during the 1999 Kocaeli and Duzce, Turkey earthquakes with resulting damage to surrounding buildings and loss of life. The potential effects of the subsequently observed poor reinforcement detailing on the dynamic response is discussed. The probable cause of the extensive damage to reinforced concrete minarets is investigated by studying the observed failure modes and their seismic performance, and through the dynamic analysis of a representative minaret. The effects of spiral stairs, door openings, and balconies on the dynamic behavior are examined. The maximum dynamic internal force demands were compared with the calculated capacities. The locations of the maximum axial, shear, and flexural demands predicted from the finite element analysis of the minaret model were consistent with the earthquake damage observed at those critical locations.
Recent strong earthquakes have shown that column failure is the primary cause of collapse in many existing older buildings and bridges. The main objective of this paper is to develop a macromodel to simulate the cyclic lateral load–deformation response of reinforced concrete columns with limited computational effort. Flexural, longitudinal bar slip, and shear deformations are predicted under monotonic lateral loads, including the effects of strength decay and stiffness degradation. Using these monotonic responses as envelopes or primary curves, cyclic responses corresponding to these three deformation components are calculated. The column under consideration is classified into one of five categories considering the potential for flexural, shear, or axial load failure. Individual cyclic responses then are combined to obtain the total lateral response of the column based on its identified failure mode. Comparison of predicted cyclic response and experimental data showed that the proposed model is sufficiently accurate.
